1. Field of the Invention
The present invention relates to a method of separating wafers into individual die for final packaging, and more particularly to an improvement in such a method using a blade for separating the die.
2. Description of the Related Art
The wafers, each being comprised of organic multiple layers on a substrate, are placed on a wafer probe, and the individual die on each wafer are tested. Those devices that function properly are left alone, while those that fail are marked. With the devices or circuits on the wafer tested, the wafers are separated into individual die for final packing. This operation is generally called "wafer scribe". A commonly used method to separate die is sawing. A rotating saw blade is used to separate the die. The rotating saw blade is drawn through the organic multiple layers and the substrate at the same time along the scribe line.
JP-A 5-95046 teaches a method of separating a wafer that is comprised of thin-film sensors attached to one side of a substrate. The substrate is formed with, by etching, holes to expose the thin-film sensors. Protection resin is painted to fill in the holes. An adhesive tape is attached to the substrate to cover the thin-film sensors to protect them during wafer scribe, by sawing, to separate die. The die are separated from the tape and the protection resin removed by dissolution. With this method, it is described that the thin-film sensors are not damaged.
Separating, in a conventional manner, a wafer involves simultaneous cutting through the organic thin film multiple layers and the substrate with the saw blade. Difference in coefficient of thermal expansion between the organic thin film layers and the substrate causes concentration of stress on a weak portion of the cutting section. The concentration of stress may cause the organic layers to peal off from the substrate if bond between the organic layers and the substrate is not tight. Further, it may cause the substrate to split to form notch in the cutting section if structural strength of the substrate is not sufficiently high.
The die that is subject to such a defect during wafer scribe will lose its commercial value, thus pushing up manufacturing cost of the tips.
An object of the present invention is to provide a method of separating wafers into individual die, which method, free from the above-mentioned problems, minimizes loss to the yield of good and reliable chips.